Battery pack

ABSTRACT

Provided is a battery pack, which can prevent easy detachment of a welded part between a cap plate and a case due to external impact, thereby enhancing hermeticity and reliability.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.2008-0038275, filed Apr. 24, 2008, the disclosure of which is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery pack, and more particularly,to a battery pack which can prevent easy detachment of a welded partbetween a cap plate and a case due to external impact, thereby enhancinghermeticity and reliability.

2. Description of the Related Art

Secondary batteries are rechargeable and can be repeatedly used. Thus,secondary batteries are more economical than disposable batteries.

Also, the secondary batteries can realize high capacity with smallvolume, so that they are widely used as a driving power source forhandheld electronic devices such as cellular phones, notebook computers,camcorders and digital cameras.

In addition, owing to the high capacity of the secondary battery, thesecondary batteries are widely used in high power products such ashybrid cars and electric tools as well as handheld electricalappliances.

Such secondary batteries include, for example, nickel-cadmium batteries,nickel-metal hydride batteries, nickel-zinc batteries, lithium ionsecondary batteries and lithium polymer secondary batteries.

The lithium secondary batteries are widely used because they are compactand have high capacity, a high operating voltage and a high energydensity per unit weight.

The lithium secondary batteries are formed by accommodating an electrodeassembly and an electrolyte in a case and sealing the case.

The lithium secondary batteries may be classified into a can type and apouch type depending on the shape of the case, and the can-typebatteries may be classified into a cylindrical type and a rectangulartype.

The rectangular-type lithium secondary battery is formed byaccommodating an electrode assembly including a positive electrodeplate, a negative electrode plate and a separator in a rectangular-typecase having an opening at one side, and sealing the opening using a capassembly.

Here, the cap assembly includes a cap plate disposed at an opening ofthe case, and an electrode terminal inserted into in the middle of thecap plate.

The case is sealed by welding an edge of the cap plate disposed at theopening using laser to join the cap plate with the case.

Since the rectangular-type secondary battery has the electrode terminalin the middle of the cap plate, the welded part between the cap plateand the case can be easily detached from each other when external impactcaused, for example, by the battery being dropped, is concentrated in apart where the electrode terminal is disposed.

Moreover, since there is a hole in the cap plate to insert the electrodeterminal into the cap plate, the hole part of the cap plate is morevulnerable to the external impact.

Recently, a rectangular-type secondary battery which has a larger widththan a height is being developed. However, when the width is larger thanthe height, the resistance to damage as a result of external impactapplied to the cap plate is relatively weak, so that the cap plate andthe case can be more easily detached from each other.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a battery pack which inhibitsdetachment of a welded part between a cap plate and a case due toexternal impact, thereby enhancing hermeticity and reliability.

According to an embodiment of the present invention, a battery packincludes: a bare cell; and a protection circuit assembly electricallyconnected with the bare cell and including a protection circuit board,wherein the protection circuit board includes a protection circuitmodule, and the protection circuit module is in contact with the barecell.

The bare cell may include a case having an opening at one side and a capassembly sealing the case. Here, the cap assembly may include a capplate coupled to the opening, and edges of the cap plate and the openingmay be welded to each other.

The case may include narrow side surfaces facing each other and wideside surfaces facing each other, these side surfaces being laterallyconnected with each other, and a first surface and a second surfaceformed by being surrounded by the side surfaces. Here, a distancebetween the narrow side surfaces facing each other may be larger than adistance between the first and second surfaces.

The protection circuit board may include a printed circuit board, and aprotection circuit, a PTC thermistor, an external connection terminaland a connection terminal which are mounted on the printed circuitboard, and the protection circuit module may be formed by covering theprotection circuit and the PTC thermistor using an encapsulating part.

The encapsulating part may be in contact with the cap plate.

The protection circuit module may be disposed in a middle part of theprotection circuit board.

The bare cell may include a welded part formed by welding an edge of thecap plate and an edge of the opening of the case, and the protectioncircuit module may be disposed on an upper surface of an edge of the capplate corresponding to the welded part.

The protection circuit module may be disposed in the middle part of thecap plate.

The cap plate may include a terminal through-hole, which iseccentrically disposed with respect to a center of the cap plate.

The terminal through-hole may be spaced ½ to ¾ apart from the center ofthe cap plate in a major axis direction.

According to another embodiment of the present invention, a battery packincludes a bare cell including a case accommodating an electrodeassembly and having an opening at one side and a cap assembly sealingthe case, and a protection circuit assembly electrically connected withthe bare cell. Here, the case includes narrow side surfaces facing eachother and wide side surfaces facing each other, these surfaces beinglaterally connected with each other, and first and second surfacesformed by being surrounded by the side surfaces. The cap assembly iscoupled to the opening and includes a cap plate having a terminalthrough-hole, a distance between the narrow side surfaces facing eachother is larger than a distance between the first and second surfaces,and the terminal through-hole is eccentrically disposed with respect toa center of the cap plate.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1A is an exploded perspective view of a battery pack according toan exemplary embodiment of the present invention;

FIG. 1B is an assembled perspective view of the battery pack of FIG. 1A;

FIG. 1C is a front view of the battery pack of FIG. 1B;

FIG. 2A is an exploded perspective view of a bare cell included in abattery pack according to an exemplary embodiment of the presentinvention;

FIG. 2B is an assembled cross-sectional view of the bare cell of FIG.2A; and

FIG. 3 is an assembled cross-sectional view of a protection circuitassembly according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIGS. 1A and 1B are exploded and assembled perspective views of abattery pack according to an exemplary embodiment of the presentinvention, respectively, and FIG. 1C is a front view of the battery packof FIG. 1B.

FIG. 2A is an exploded perspective view of a bare cell included in abattery pack according to an exemplary embodiment of the presentinvention, and FIG. 2B is an assembled cross-sectional view of the barecell of FIG. 2A.

Referring to FIGS. 2A and 2B, the bare cell 100 includes a case 10, anelectrode assembly 20 accommodated in the case 10, and a cap assembly 30sealing the case 10.

The bare cell 100 further includes an insulating case 40 disposed on theelectrode assembly 20 accommodated in the case 10.

The bare cell 100 further includes an electrolyte accommodated in thecase 10 to help the current flow.

The case 10 may form an appearance of the bare cell 100, which may beformed in a rectangular shape or a rectangular shape having roundedcorners, but the present invention is not limited thereto.

Here, one side of the case 10 has an opening for inserting the electrodeassembly 20 into the case 10.

To be more specific, the case 10 includes narrow side surfaces facingeach other and wide side surfaces facing each other, which are connectedwith each other.

Among surfaces formed by being surrounded by the four side surfaces, afirst surface is open to insert the electrode assembly 20 into the case10, and a second surface is closed.

Hereinafter, the open first surface is called a top surface of the case10, and the close second surface is called a bottom surface of the case10.

A lateral width W1 of the bare cell 100 is a distance between the narrowside surfaces facing each other, and a longitudinal width W2 of the barecell 100 is a distance between the top surface and the bottom surface.

Here, the lateral width W1 is larger than the longitudinal width W2.

The case 10 may be formed of a metallic material, for example, oneselected from aluminum, an aluminum alloy, stainless steel andequivalents thereof.

The electrode assembly 20 includes a first electrode plate 21 and asecond electrode plate 23, which have different polarities from eachother.

The electrode assembly 20 further includes a separator 25 interposedbetween the first and second electrode plates 21 and 23, and theseparator 25 prevents a short circuit between the two electrode plates21 and 23.

Hereinafter, the first electrode plate 21 is called a positive electrodeplate, and the second electrode plate 23 is called a negative electrodeplate.

The positive electrode plate 21 is formed by applying a slurrycontaining a positive electrode active material to a positive electrodecollector, and the negative electrode plate 23 is formed by applying aslurry containing a negative electrode active material to a negativeelectrode collector.

Each of the positive and negative electrode plates 21 and 23 includes anon-coated portion to which an active material is not applied, and eachelectrode tab 27 or 29 is attached to the non-coating portion to beelectrically connected.

That is, the first electrode tab 27 is electrically connected with thepositive electrode plate 21, and the second electrode tab 29 iselectrically connected with the negative electrode plate 23.

Hereinafter, the first electrode tab 27 is called a positive electrodetab, and the second electrode tab 29 is called a negative electrode tab.

The cap assembly 30 may include a cap plate 31, an insulating gasket 32,an electrode terminal 33, an insulating plate 34, a terminal plate 35and an electrolyte inlet plug 36.

The cap plate 31 is disposed at an opening of the case 10 and an edge 31d of the cap plate 31 is joined with an edge 11 of the opening of thecase 10 by welding, e.g. laser welding, thereby sealing the case 10.

Therefore, the bare cell 100 includes a welded part 50 formed by weldingan edge 31 d of the cap plate 31 and an edge 11 of the opening of thecase 10, and the case 10 and the cap plate 31 are fixed by the weldedpart 50.

The cap plate 31 includes a terminal through-hole 31 a into which theinsulating gasket 32 and the electrode terminal 33 are inserted, and anelectrolyte inlet 31 b serving as a passage for electrolyte injection.

Here, the terminal through-hole 31 a may be eccentrically disposed withrespect to the center of the cap plate 31, and may be formed adjacent toan end in a major axis direction.

Thus, the electrode terminal 33 coupled to the terminal through-hole 31a is also eccentrically disposed with respect to the center of the capplate 31, and a space is formed in the middle of the cap plate 31.

As shown in FIG. 3. in the middle of the cap plate 31, a protectioncircuit 212 and a PTC 213 covered by an encapsulating part 218 to bedescribed later, i.e., a protection circuit module 219 is disposed.

When the terminal through-hole 31 a is disposed too close to the end ofthe cap plate 31 in the major axis direction, a space for elements to bedisposed under the cap plate 31 becomes smaller.

Alternatively, when the terminal through-hole 31 a is disposed close tothe center of the cap plate 31, a space for the protection circuitmodule 219 becomes smaller.

Thus, the terminal through-hole 31 a may be spaced from the approximatecenter of the cap plate ½ to ¾ of the distance of the cap plate 31 fromthe approximate center to the approximate end of the cap plate 31 in themajor axis direction.

Here, the electrode terminal 33 is also disposed adjacent to the end ofthe cap plate 31 in the major axis direction, so that impact applied tothe electrode terminal 33 can be scattered as compared with when theelectrode terminal 33 is disposed in the middle of the cap plate 31.

The cap plate 31 may include a vent 31 c which is broken to exhaust agas when inner pressure of the bare cell 100 is increased, and the vent31 c may include a notch part to facilitate the breakage of the vent 31c.

The insulating gasket 32 is coupled to the terminal through-hole 31 aformed in the cap plate 31, and insulates the electrode terminal 33 fromthe cap plate 31.

In addition, the insulating gasket 32 has a hole in the middle part, andthe electrode terminal 33 is positioned in the hole.

A lower part of the electrode terminal 33 is electrically connected withthe terminal plate 35 through the cap plate 31.

The insulating plate 34 is disposed under the cap plate 31, andinsulates the terminal plate 35 from the cap plate 31.

In addition, the insulating plate 34 has a hole to connect the terminalplate 35 with the electrode terminal 33.

The terminal plate 35 is disposed under the insulating plate 34, andconnected with the electrode terminal 33 to form an electrical path.

Further, the positive electrode tab 27 is electrically connected with abottom surface of the cap plate 31, and the negative electrode tab 29 iselectrically connected with a bottom surface of the terminal plate 35.

The insulating case 40 is disposed on the electrode assembly 20accommodated in the case 10 to prevent movement of the electrodeassembly 20.

The insulating case 40 includes a tab groove 41 and a tab hole 42, bothof which separate the positive electrode tab 27 a predetermined distancefrom the negative electrode tab 29 to prevent a short circuittherebetween and serve as guides when the positive and negativeelectrode tabs 27 and 29 project through the insulating case 40.

The insulating case 40 may further include an injection hole 43 formedto provide a passage for smooth injection of the electrolyte into theelectrode assembly 20.

Referring to FIGS. 1A to 1C, a battery pack 1 according to an exemplaryembodiment of the present invention includes a bare cell 100 and aprotection circuit assembly 200, which are electrically connected witheach other.

As described with reference to FIG. 2, the bare cell 100 is sealed byjoining an open top surface of the case 10 with the cap assembly 30.

Hereinafter, the top surface of the case 10 coupled to the cap assembly30 is called a top surface of the bare cell 100, and the protectioncircuit assembly 200 may be disposed on the top surface of the bare cell100.

Here, at the top surface of the bare cell 100, the electrode terminal 33is disposed adjacent to an end of the bare cell 100 in a major axisdirection.

FIG. 3 is an assembled cross-sectional view of a protection circuitassembly according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the protection circuit assembly 200 includes aprotection circuit board 210, and lead plates having a first lead plate230 and a second lead plate 250 for electrical connection between theprotection circuit board 210 and the bare cell 100.

The protection circuit board 210 may be formed by mounting a protectioncircuit 212, a PTC thermistor 213, an external connection terminal 214,and connection terminals having a first connection terminal 215 and asecond connection terminal 216 for connecting the lead plates 230 and250 on a printed circuit board 211.

The protection circuit board 210 further includes a terminal hole 217formed at a location corresponding to the electrode terminal 33 of thebare cell 100, and the terminal hole 217 may be formed adjacent to anend of a long side of the printed circuit board 211.

Here, the protection circuit 212 and the PTC thermistor 213 are disposedin a middle region of the protection circuit board 210, and covered byan encapsulating part 218.

A protection circuit module 219 is formed by covering the protectioncircuit 212 and the PTC thermistor 213 using the encapsulating part 218.

The encapsulating part 218 may be formed of resin, for example, anorganic material including a hardener and epoxy forming athree-dimensional hardening structure by being hardened due to heat, oran organic-inorganic combination material to improve mechanical andelectrical performance.

The protection circuit 212 may include a circuit for controlling chargeand discharge of the bare cell 100, a circuit for controlling anabnormal operation such as overcharge, overdischarge or overcurrent, anda smart circuit for providing information including available time,remaining charge time, remaining charge amount and life span of the barecell 100.

Here, as illustrated in FIG. 1C, a lower end of the protection circuitmodule 219 is in contact with the cap plate 31 of the bare cell 100.

Due to the protection circuit module 219, external impact applied to awelded part between the cap plate 31 and the case 10 can be reduced.

Also, the protection circuit module 219 may be disposed on an uppersurface of the cap plate 31 wherein the edge 31 d of the cap plate 31 iscoupled to the welded part 50 formed between the edge 31 d of the capplate 31 and the edge 11 of the opening of the case 10.

Therefore, even if there is external impact, the protection circuitmodule 219 serves as a support, which thus may inhibit detachment of thewelded part 50.

The first lead plate 230 is connected with the first connection terminal215 and exposed outside through the terminal hole 217, and the secondlead plate 250 is connected with the second connection terminal 216.

In the battery pack 1 (FIG. 1A) according to one exemplary embodiment ofthe present invention, the first lead plate 230 is connected with theelectrode terminal 33, and the second lead plate 250 is connected withthe cap plate 31, so that the bare cell 100 is electrically connectedwith the protection circuit assembly 200.

Table 1 shows results of a free drop test for a conventional batterypack and a battery pack according to the exemplary embodiment of thepresent invention, in both of which a case and a cap plate are weldedwith an equal weld depth.

TABLE 1 Free Drop Test Weld Depth Comparative Cycle (μm) ExampleEmbodiment 1 225 300 500 2 237 400 500 3 238 400 500 4 242 400 500 5 244400 500 6 246 400 600 7 247 500 600 8 256 500 600 9 257 500 600 10 259500 600 11 265 500 600 12 267 500 600 13 269 500 600 14 271 500 600 15273 500 600 16 275 500 700 17 283 500 700 18 285 500 600 19 292 600 70020 296 600 800 21 297 600 800

That is, in the comparative example, after a battery pack in which abare cell having an electrode terminal disposed in the middle of a capplate is connected with a protection circuit board is subjected to afree drop test, generation of a crack in a welded part between a caseand the cap plate is expressed in hundreds.

In the present embodiment, after a battery pack in which a bare cellhaving an electrode terminal disposed adjacent to an end of a cap platein a major axis direction is formed in contact with a protection circuitmodule in a middle of the bare cell is subjected to a free drop test,generation of a crack in a welded part between a case and the cap plateis expressed in hundreds.

In Cycle 1, the results of the free drop test show that the battery packin the comparative example satisfies 300 cycles, but not 400 cycles, butthe battery pack in the present embodiment satisfies 500 cycles.

In Cycle 2, the results of the free drop test show that the battery packin the comparative example satisfies 400 cycles, but not 500 cycles, butthe battery pack in the present embodiment satisfies 500 cycles.

Similarly, in other cases, the battery pack in the present embodimentshows a better characteristic than that in the comparative example inthe free drop test.

Of course, as shown in Table 1, as the weld depth becomes deeper, thebattery pack in the present embodiment generally shows a bettercharacteristic in the free drop test.

However, since a larger output is required in welding to further deepenthe weld depth, additional equipment and cost are needed.

Further, the larger output can damage an insulating case and anelectrode assembly.

The battery pack 1 according to the exemplary embodiment of the presentinvention may further include a shock-absorber 300 disposed between thecap plate 31 and the protection circuit module 219.

The shock-absorber 300 may be disposed to cover the welded part toreduce impact applied to the welded part between the case 10 and the capplate 31.

The shock-absorber 300 may be a double-sided adhesive tape, and mayimprove adhesive strength between the cap plate 31 and the protectioncircuit module 219.

The battery pack 1 formed as such may further include a hard caseaccommodating the bare cell 100 and the protection circuit assembly 200.

Alternatively, the battery pack 1 may be subjected to tubing andlabeling to cover the bare cell 100 and the protection circuit assembly200 while the protection circuit assembly 200 is covered by an uppercover.

Consequently, a protection circuit module is in contact with a barecell, and thus external impact applied to a welded part between a capplate and a case can be reduced.

Further, an electrode terminal may be disposed adjacent to an end of thebare cell in a major axis direction, thereby dispersing the impactapplied to the welded part between the cap plate and the case. Thus,easy detachment of the cap plate from the case due to external impactcan be prevented.

Also, the welded part is not easily detached, thereby enhancinghermeticity and reliability.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A battery pack, comprising: a bare cell; and a protection circuitassembly electrically connected with the bare cell and including aprotection circuit board, wherein the protection circuit board includesa protection circuit module, and the protection circuit module is incontact with the bare cell such that the contact of the bare cell andthe protection circuit module inhibits damage to the bare cell as aresult of application of external forces to the bare cell.
 2. Thebattery pack according to claim 1, wherein the bare cell includes a casehaving an opening at one side and a cap assembly sealing the case, thecap assembly includes a cap plate coupled to the opening, and edges ofthe cap plate and the opening are welded to each other.
 3. The batterypack according to claim 2, wherein the case includes narrow sidesurfaces facing each other and wide side surfaces facing each other,these side surfaces being laterally connected with each other, and afirst surface and a second surface formed by being surrounded by theside surfaces, and a distance between the narrow side surfaces facingeach other is larger than a distance between the first and secondsurfaces.
 4. The battery pack according to claim 2, wherein theprotection circuit board includes a printed circuit board, and aprotection circuit, a PTC thermistor, an external connection terminaland a connection terminal which are mounted on the printed circuitboard, and the protection circuit module is formed by covering theprotection circuit and the PTC thermistor using an encapsulating part.5. The battery pack according to claim 4, wherein the encapsulating partis formed of resin.
 6. The battery pack according to claim 4, whereinthe encapsulating part is in contact with the cap plate.
 7. The batterypack according to claim 1, wherein the protection circuit module isdisposed in a middle part of the protection circuit board.
 8. Thebattery pack according to claim 2, wherein the bare cell includes awelded part formed by welding an edge of the cap plate and an edge ofthe opening of the case, and wherein the protection circuit module isdisposed on an upper surface of the cap plate that has the edge coupledto the welded part.
 9. The battery pack according to claim 8, whereinthe protection circuit module is disposed in a middle part of the capplate.
 10. The battery pack according to claim 2, wherein the cap plateincludes a terminal through-hole, which is eccentrically disposed withrespect to the center of the cap plate.
 11. The battery pack accordingto claim 10, wherein the terminal through-hole is spaced from theapproximate center ½ to ¾ of the distance between the approximate centerand the end of the cap plate in a major axis direction.
 12. The batterypack according to claim 1, further comprising: a shock-absorber disposedbetween the protection circuit module and the bare cell.
 13. The batterypack according to claim 12, wherein the shock-absorber includes adouble-sided adhesive tape.
 14. A battery pack, comprising: a bare cellincluding a case accommodating an electrode assembly and having anopening at one side and a cap assembly sealing the case; and aprotection circuit assembly electrically connected with the bare cell,wherein the case includes narrow side surfaces facing each other andwide side surfaces facing each other, these surfaces being laterallyconnected with each other, and first and second surfaces formed by beingsurrounded by the side surfaces, wherein the cap assembly is coupled tothe opening and includes a cap plate having a terminal through-hole,wherein a distance between the narrow side surfaces facing each other islarger than a distance between the first and second surfaces, andwherein the terminal through-hole is eccentrically disposed with respectto the center of the cap plate.
 15. The battery pack according to claim14, wherein edges of the cap plate and the opening are welded to eachother.
 16. The battery pack according to claim 14, wherein the terminalthrough-hole is disposed adjacent to an end of the cap plate in a majoraxis direction.
 17. The battery pack according to claim 16, wherein theterminal through-hole is spaced from the approximate center ½ to ¾ ofthe distance between the approximate center and the end of the cap platein the major axis direction.
 18. The battery pack according to claim 15,wherein the protection circuit assembly includes a protection circuitboard and a lead plate to electrically connect the protection circuitboard with the bare cell, and the protection circuit board includes aprinted circuit board, and a protection circuit, a PTC thermistor, anexternal connection terminal and a connection terminal which are mountedon the printed circuit board, and an encapsulating part covering theprotection circuit and the PTC thermistor.
 19. The battery packaccording to claim 18, wherein the protection circuit, the PTCthermistor and the encapsulating part are disposed in a middle part ofthe protection circuit board.
 20. The battery pack according to claim19, wherein the encapsulating part is in contact with the cap plate. 21.The battery pack according to claim 19, wherein the encapsulating partis formed of resin.
 22. The battery pack according to claim 18, whereinthe bare cell includes a welded part formed by welding an edge of thecap plate and an edge of the opening of the case, and wherein theencapsulating part is disposed on an upper surface of the cap plate thathas the edge coupled to the welded part.
 23. The battery pack accordingto claim 22, wherein the encapsulating part is disposed in the middlepart of the cap plate.